The present invention generally relates to solid phase immunoassay test devices whether the sandwich or competition type for providing sensitive detection of an analyte in a biological fluid sample and is more particularly directed to a colored contrast system therefore. Solid phase immunoassay test devices incorporate a solid support to which one member of the ligand-receptor pair, usually an antibody, antigen, or hapten is bond.
Lateral flow immunoassay tests in typical use today, generally include a porous component of nitrocellulose membrane, as the solid, with specific reagent applied onto specific zones therein.
An upstream zone usually includes a specific binding reagent for the analyte being tested, conjugated to a visible label such as a gold colloid or colored latex particle. The labeled reagent is formulated to facilitate its released from the membrane after the sample is applied to the test strip.
In typical competition assays, a sample containing analyte is introduced to a sample area of the test strip. Migration of the sample, caused by the capillary wicking within the porous membrane, re-suspends the labeled reagent from its stationary position on the strip. As the reagent mixture migrates along the strip it is brought into contact with the immobilized capture reagent. If the analyte is present in the sample, binding to the labeled reagent (Antibody-visual label) will take place during this migration.
If the amount of analyte is enough to exhaust all binding sites on the labeled reagent, binding of the visual label to the capture reagent will not occur. This constitutes a positive result.
If there is no analyte in the sample, the visual label will bind at the capture stripe producing a negative result seen as a colored band or strips.
For the most part, these tests are interpreted visually by human eye to determine the presence or absence of an analyte (drug). Membranes like nitrocellulose provide a white background to visualize the presence or absence of the colored line or stripe. Presently, white in the only color commercially available for nitrocellulose membrane.
Partial sight, aging, and congenital color deficits can produce changes in perception that reduce the visual effectiveness or certain color combinations.
The present invention provides for lateral flow immunoassay device utilizing complementary colors to provide better contrast for visual perception of test results.
A lateral flow immunoassay device in accordance with the present invention generally includes a porous strip for enabling capillary migration of a fluid sample therealong. A labeled reagent is disposed on the stripe with the label reagent being formulated for suspension in the sample migrating therepast. A captive reagent is immobilized on the strip in a path of the sample migration with the captive reagent being formulated to bind to the labeled reagent to form a visual colored site on the strip.
Also included are means for providing a complimentary color background for the colored site in order to increase visual perception of the colored site.
In one embodiment of the present invention, the means for providing a complimentary color background comprises a dye incorporated into the porous strip. In another embodiment of the present invention a means for providing a complementary color background comprises a transparent colored film disposed over the porous strip. The film may be in direct contact with the strip by adhesive or suspended over the strip in close proximity therewith with minimal or no contact with the strip.
When a white porous nitrocellulose membrane is used for the porous strip, the means in accordance with the present invention is, in effect an element for changing the white strip to a color which enhances a visual perception of the colored site.
The nitrocellulore membrane may be formed on a Mylar backing, as is well known in the art. In the case of the present invention this Mylar backing may be an optically clear yellow Mylar and membrane viewed through the Mylar backing as will be discussed hereinafter.
In the embodiment in which a film is utilized, the latter may be laminated or adhered to the porous strip or spaced apart therefrom as hereinabove noted.
More specifically, when the colored site is blue, the complementary color background may be selected from a group consisting of yellow, yellow-orange and orange.
Alternative complimentary color combination that may be utilized such as a green background when the colored site is red.
The present also provides for an improvement in existing lateral flow immunoassay devices having a strip for enabling capillary migration of a fluid sample therethrough, a label, reagent disposed on the strip and formulated for suspension in the sample migrating therepast, and a captive agent immobilized on the strip in a path of sample migration and formulated to bind with the label reagent to form a visible site on the strip. The improvement comprises a colored background for enhancing the color perception of the colored site which, may be, for example, a dye incorporated into the strip or a transparent film of a selected background color either directly laminated to the nitrocellulose strip by pressure sensitive adhesive or suspended barely above the strip with minimal or no contract with the strip, facilitated by a die-cut thin plastic carrier, or the like.
A method in accordance with the present invention for enhancing visual perception of a colored site in a immunoassay device includes dying the strip a color which is complimentary to the colored site produced by binding of the labeled reagent and the capture reagent or the step of providing a transparent film having a color which is complimentary to the colored site.